Delta/Notch signaling is an important inductive pathway in the development of many different cell types in the embryos of most animals, including echinoderms. Using sea urchin embryos, a variety of techniques, including methods in molecular biology, microsurgery and microscopy, can be combined to answer important questions about development. The echinoderm phylum is also in a close evolutionary position relative to the vertebrates, and provides a unique model for studying the evolution of deuterostome development. The long-term goal of this research is to examine the evolution of mesoderm development within the echinoderm phylum. The embryos of derived sea urchins have four micromeres at the vegetal pole that have powerful organizing abilities. Our recent studies show that the normal role of Delta in derived sea urchins is to induce mesoderm; the micromere descendants express Delta; and Delta expression alone is sufficient to organize the whole embryo. The embryos of primitive sea urchins have variable numbers of micromeres and mesoderm in these embryos forms much later than in derived sea urchins. These features suggest that there are significant differences in mesoderm development and that the micromeres may not play as critical a role in development as in derived sea urchins. The research proposed here will identify the role of Delta and other inductive pathways involved in the development in the primitive sea urchin. There are four specific aims. (1) We will characterize the expression pattern of Delta. We hypothesize that Delta will be expressed at a later time; Delta may or may not be expressed by micromere descendants. (2) We will use overexpression and knockdown experiments to examine the function of Delta. These misexpression experiments will be combined with microsurgery to examine Delta function in specific cells in the context of an otherwise normal embryo. (3) We will use fate mapping techniques to pinpoint the origin of mesoderm. We hypothesize that that several types of mesoderm will originate from the micromeres. (4) We will examine whether the micromeres are necessary and/or sufficient for mesoderm development and the development of other cell types. We will also examine the timing of putative micromere induction. By focusing on the development of a primitive sea urchin, this research will begin to provide insight on how the Delta/Notch signaling pathway and mesoderm development have evolved within the echinoderm phylum. [unreadable] [unreadable] [unreadable]